INTERACTION OF GEOMETRICAL KINKS WITH HYDROGEN FOR SCREW DISLOCATIONS IN IRON

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INTERACTION OF GEOMETRICAL KINKS WITH HYDROGEN FOR SCREW DISLOCATIONS IN IRON

J. San Juan, M. Nó, Gilbert Fantozzi, C. Esnouf

To cite this version:

J. San Juan, M. Nó, Gilbert Fantozzi, C. Esnouf. INTERACTION OF GEOMETRICAL KINKS

WITH HYDROGEN FOR SCREW DISLOCATIONS IN IRON. Journal de Physique Colloques, 1987,

48 (C8), pp.C8-191-C8-196. �10.1051/jphyscol:1987826�. �jpa-00227130�

JOURNAL DE PHYSIQUE

Colloque C8, suppl6ment a u n012, Tome 48, dkcembre

1987

INTERACTION OF GEOMETRICAL KINKS WITH HYDROGEN FOR SCREW DISLOCATIONS I 1 IRON

J. S A N JUAN, M.L.

~ 6 ,

^G. FANTOZZI* and C. ESNOUF"

Dpto de ~l/sica del Estado ~ G l i d o , Facultad de Ciencias, Universidad del Pais Vasco, Aptdo 644, SP-48009 Bilbao, Spain

* ~ r o u p e d'Etudes de MBtallurgie Physique et de Physique des Materiaux, LA-341, INSA Bdt. 502, F-69621 Villeurbanne Cedex, France

Resume' - Les mesures de frottement intefrieur e t de module r e a l i s g e e

cE

basse temp4ra- t u r e pour diff&rentes concentrations en hydrogdne ont montre' que l a composante a'

du

pic a dans l e f e r apparait, pour un large domaine de concentrations en hydrogdne, au mgme temps que l a r e l a x a t i o n Snoek-Koster ( H ) . Ces r b u l t a t s nous pennettent de conclure que l a m o b i l i t g des de'crochements ggome'triques sur Zes d i s l o c a t i o n s v i s e s t t r d s peu modifige par Zes atomes d7aydrogdne. N6anrnoins, l ' i n t e r a c t i o n des de'croche- ments gdome'triques sur l e s d i s l o c a t i o n s v i s avec des amas d 'hydrogdne diatomiques e s t importanteet donne l i e u

ci

un processus de r e h a t i o n q u i participe

ci

l a composan-.

t e SK2 de l a relaxation SKfH).

Abstract - Measurements o f i n t e r n a l f r i c t i o n and modulus a t low temperature f o r d i f - ferent amounts o f hydrogen have shorn t h a t t h e a'component of t h e a peak i n Iron can appear simultaneously w i t h t h e S-K(H) peak for a large range of amount o f hydrogen.

These r e s u l t s allow u s t o conclude t h a t t h e geometrical kink mobility on screw d i s l o - c a t i o n s i s only weakly modified by t h e hydrogen atoms. Nevertheless t h e i n t e r a c t i o n of geometrical k i n k s on screw d i s l o c a t i o n s and diatomic hydrogen c l u s t e r s i s n o t i - ceable and causes a r e l a x a t i o n process t h a t c o n t r i b u t e s t o t h e SK2 component o f SKIH) r e l a z a t i o n .

I.- INTRODUCTION

The intrinsic mobility of dislocations is strongly modified by means of the pre- sence of hydrogen in iron. Indeed, the

a

peak, due to kink pair formation (KPF) on non-screw dislocations, disappears to give way to Snoek-KCster(H) relaxation which is constituted by two components, SKI around llOK and SK2 at about 155K (for 1Hz).

The experimental characteristics of the SK(H) relaxation have been studied in various papers (1-9). The theoretical interpretation of these components has been reviewed in a recent paper (lo), which gives a new analysis of the SK(H) relaxation according to all experimental characteristics. In this sense,it can be stated that the SKI com- ponent is due to thermally activated kink formation on the non-screw dislocations controlled by the diffusion of the hydrogen atoms situated along the dislocation line. A more precise analysis of SK2 component, which historically has aroused more controversy, has allowed us to exclude the interpretations of KPF on the screw dis- locations controlled by the diffusion of the hydrogen atoms, which were proposed by Hirth (ll),as well as the longitudinal diffusion of the hydrogen atoms proposed by Ritchie (12). In this way, we have pointed out that the SK2 component is due to the same process as the SKI

,

but is controlled by the diffusion of small clusters of hydrogen (probably diatomic in nature). On tne other hand, recently, internal fric- tion experiments with a static stress have clearly shown that the

a'

component si- tuated on the low temperature side of the

a

peak can be attributed to the geometri- cal kink migration (GKM) on screw dislocations (to be published)/ZO/. Therefore, if this a'component also disappears due to the addition of hydrogen, one could think that the interaction process of geometrical kinks on screw dislocations with hydro- gen should also contribute of SK(H) relaxation as was suggested by Vetter et al.

(13) in order to explain SK2 component.

In this paper we have carried outexperimentswith high purity Iron doped with

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987826

JOURNAL DE PHYSIQUE

i n t e r a c t i o n of g e o m e t r i c a l k i n k s on screw d i s l o c a t i o n s w i t h hydrogen. Indeed, f o r small amounts o f hydrogen, t h e a' component c o e x i s t s w i t h t h e SK(H1 r e l a x a t i o n ; howe- v e r c o n c e r n i n g l a r g e a m o u n t s o f hydrogen, it seems c l e a r t h a t t h e i n t e r a c t i o n p r o c e s s of g e o m e t r i c a l k i n k s w i t h hydrogen c o n t r i b u t e t o t h e SK(H) r e l a x a t i o n .

11.- EXPERIMENTAL PROCEDURE

The measurements a r e made i n an i n v e r t e d pendulum d e s c r i b e d elsewhere (8,141, o n p l a t e s (0.5x5x40mm) of CENG p u r e i r o n ( 1 5 ) . We have a p p l i e d an a x i a l magnetic f i e l d of 2 0 0 O e i n o r d e r t o e l i m i n a t e t h e e f f e c t s of t h e m a g n e t o e l a s t i c damping. The mea- surements were made a t a mean s t r a i n amplitude of 5 x 1 0 - ~ .

The samples had been pre-deformed t o 5% i n t r a c t i o n a t room temperature (RT) s o a s t o s u p p r e s s t h e peak, and l a t e r t h e y were deformed to 5% i n t o r s i o n a t RT.

Afterwards t h e hydrogen was i n t r o d u c e d i n t o t h e samples by e l e c t r o l y t i c c h a r g i n g i n a s o l u t i o n 5% of H2S04 w i t h a few drops of CS2 a s c a t a l y t i c a g e n t , d u r i n g 15 minutes a t 400mA.

I n o r d e r t o o b t a i n d i f f e r e n t c o n c e n t r a t i o n s o f hydrogen, e l e c t r o l y t i c charging was c a r r i e d o u t by means o f two p r o c e d u r e s :

a ) To o b t a i n low c o n c e n t r a t i o n s , t h e charging was done a t R.T., mounting t h e sample i n t h e pendulum a t RT a s w e l l and t h e n c o o l i n g t h e c r y o s t a t .

b ) To o b t a i n high c o n c e n t r a t i o n s , t h e c h a r g i n g was done a t 250K, mounting t h e sample i n t h e pendulum a t 78K. having cooled t h e c r y o s t a t p r e v i o u s l y .

111.- RESULTS AND DISCUSSION

F i r s t l y , we measured an i n t e r n a l f r i c t i o n spectrum of a p u r e i r o n sample which had been deformed t o 5% by t r a c t i o n and 5% by t o r s i o n and we n o t i c e d only t h e

a

peak ( f i g - l a ) wich i s r e p r e s e n t e d a f t e r e l i m i n a t i n g t h e background. Then we char- ged t h e sample w i t h a s m a l l amount of hydrogen and a s a consequence of t h i s , a r e l a - t i v e l y small SK(H) r e l a x a t i o n appeared i n t h e i n t e r n a l f r i c t i o n spectrum ( f i g . l b ) . I t can b e observed t h a t SK(H) r e l a x a t i o n corresponds almost e x c l u s i v e l y t o SKI compo- n e n t ; furthermore, t h e a peak which was a t t r i b u t e d t o KPF on non-screw d i s l o c a t i o n s h a s disappeared almost completely e x c e p t f o r t h e a - component a t l o y t e m p e r a t u r e , which was r e c e n t l y acknowledged a s GKM on screw d i s l o c a t i o n s ( t o be p u b l i s h e d ) . Such a' peak does n o t d e c r e a s e a s can b e o b s e r v e d i n t h e l e v e l s of i n t e r n a l f r i c t i o n a f t e r e l i m i n a t i n g t h e background. Both e f f e c t s a r e a l s o shown i n t h e c u r v e s o f t h e s h e a r nndulus ( f i g . 2 ) where we c a n o b s e r v e t h a t a f t e r hydrogen charging (curve b ) , t h e r e i s s t i l l a modulus d e f e c t below 20K. which corresponds t o t h e

a'

component. On t h e o t h e r hand, t h e modulus d e f e c t a s s o c i a t e d w i t h SK(H) r e l a x a t i o n i s f a r s m a l l e r than t h e modulus d e f e c t a s s o c i a t e d w i t h t h e former a peak (curve a ) . Such f a c t s i n - d i c a t e t h a t non-screw d i s l o c a t i o n s a r e hydrogen-blocked s o a s t o p r e v e n t t h e

a

peak from a p p e a r i n g ; however t h e c o n c e n t r a t i o n o f hydrogen atoms a l o n g t h e d i s l o c a t i o n l i n e i s r e l a t i v e l y low and t h u s S K ( H ) r e l a x a t i o n does n o t r e a c h i t s maximum s t r e n g t h and i s s i g n i f i c a n t l y s h i f t e d towards low t e m p e r a t u r e s , a s it was p r e d i c t e d t h e o r e t i - c a l l y .

Afterwards we charged t h e sample w i t h l a r g e amounts of hydrogen u n t i l we ob- t a i n e d a n o v e r s a t u r a t i o n above t h e e q u i l i b r i u m p o i n t ( 6 (SK) > 4 0 x 1 0 - ~ 1 . Such over- s a t u r a t i o n i s t h e o r i g i n of some t r a n s i t o r y e f f e c t s on t h e i n t e r n a l f r i c t i o n spec- trum which a r e n o t t h e s u b j e c t o f t h i s paper and consequently w i l l be d e a l t w i t h i n a n o t h e r paper. Due t o a n n e a l i n g . a t 240K v e r y slowly t h e system r e a c h e s an

" e q u i l i b r i u m c o n c e n t r a t i o n " , t h a t i s t o s a y , t r a n s i t o r y e f f e c t s d i s a p p e a r and t h e b a s i c o u t l o o k of t h e i n t e r n a l f r i c t i o n spectrum o c c u r s r e c u r r e n t l y and p e r f e c t l y . Such i n t e r n a l f r i c t i o n spectrum i s shown i n f i g . 3 a where a s i g n i f i c a n t l y developed SK(H) r e l a x a t i o n c a n be observed w i t h a n i m p o r t a n t SK2 Component- However t h e u'com- ponent of

a

peak h a s disappeared a l m o s t completely. Indeed, t h e curve o f t h e c o r r e s - ponding s h e a r modulus, f i g . 4 a , does n o t show any modulus d e f e c t a t low t e m p e r a t u r e s ; furthermore, i f we compare c u r v e s a and c i n f i g . 4 we can n o t i c e t h a t t h e modulus d e f e c t of SK(H) r e l a x a t i o n e q u a l s t h a t o f t h e former a peak. T h i s i n d i c a t e s t h a t under such c o n d i t i o n s , SK(H) r e l a x a t i o n h a s reached i t s maximum e q u i l i b r i u m s t r e n g t h - T h e r e f o r e , we c o u l d t h i n k a f t e r a f i r s t look a t t h e r e s u l t s , t h a t t h e d i s a p p e a r a n c e o f a'component i s r e l a t e d t o t h e appearance of SX? component. However, such assump-

t i o n i s n o t t o t a l l y c o r r e c t , a s we w i l l now prove.

A f t e r a slow d e g a s s i n g a t 240K b o t h peaks have decreased (fig.3b1, b u t a t t h e

same time t h e a - component h a s developed a t low temperatures. T h i s e f f e c t can be c l e a r l y seen i n t h e c u r v e of t h e corresponding s h e a r modulus, f i g . 4 b . I f we a n a l y s e t h e curve of t h e modulus i n d e t a i l and compare it w i t h t h e curve o b t a i n e d b e f o r e degassing, it can be observed t h a t t h e modulus d e f e c t corresponding t o SKI component h a s undergone almost n o changes a f t e r and b e f o r e t h e degassing p r o c e s s , whereas t h e modulus d e f e c t a s s o c i a t e d w i t h SK2 compqnent h a s decreased by an amount e q u a l t o t h e modulus d e f e c t a s s o c i a t e d w i t h t h e a'component. Indeed, t h e d i f f e r e n c e between c u r v e s a and b i s approximately t h e same a t 20K and 130K ( i n d i c a t e d by means of arrows i n f i g . 4 )

.

These f a c t s confirm t h e co-existence o f a'and t h e SKI component shown i n f i g . 1 , and they seem t o i n d i c a t e t h a t t h e appearanceand disappearance of t h e a ' component i s n o t a s s o c i a t e d w i t h such SKI component. Therefore we could i n f e r t h a t t h e i n t e r - a c t i o n p r o c e s s o f hydrogen w i t h t h e geometrical k i n k s on screw d i s l o c a t i o n s does n o t c o n t r i b u t e t o t h e SKI component of t h e SK(H) r e l a x a t i o n .

N e v e r t h e l e s s , t h e appearance of t h e a- component i s accompanied by t h e d e c r e a s e of SK2 component by a n e q u i v a l e n t amount, a s i t i s shown by t h e modulus d e f e c t curves. Thus we could deduce t h a t geometrical k i n k s on screw d i s l o c a t i o n s i n t e r a c t w i t h hydrogen and produce a r e l a x a t i o n p r o c e s s t h a t c o n t r i b u t e s t o t h e SK2 component of t h e SK(H) r e l a x a t i o n . However, we must remark t h a t such i n t e r a c t i o n i s n o t t h e Only p r o c e s s r e s p o n s i b l e f o r t h e o r i g i n o f t h e SIC2 component. I n f a c t , i f we compare t h e i n t e r n a l f r i c t i o n l e v e l s a t low temperature we can s e e t h a t i n t e r n a l f r i c - t i o n i n f i g . 3 b i s approximately t h e same a s t h a t shown i n f i g . l b , which i n d i c a t e s t h a t t h e a - component h a s r e g a i n e d i t s maximum s t r e n g t h and t h e r e f o r e t h e geometri- c a l k i n k s do n o t i n t e r a c t w i t h hydrogen any more. However, SK2 component s t i l l h a s a n o t i c e a b l e s t r e n g t h t h a t can only be a t t r i b u t e d t o t h e K.P.F. p r o c e s s c o n t r o l l e d by t h e d i f f u s i o n of p a i r s of hydrogen atoms ( 1 0 ) . I n t h i s c a s e , looking a t t h e cur- v e s showing t h e modulus d e f e c t , we can e s t i m a t e t h e c o n t r i b u t i o n t o t h e SK2 compo- n e n t a s 40% by G.K.M. p r o c e s s and a 60% by K.P.F. p r o c e s s a l t h o u g h s u c h f i g u r e s a r e n o t meaningful s i n c e t h e y l a r g e l y depend on t h e s t r u c t u r e of t h e d i s l o c a t i o n n e t - work and on t h e c o n c e n t r a t i o n of hydrogen c l u s t e r s .

A f t e r o b t a i n i n g t h e s e r e s u l t s , i t seems t o be c l e a r t h a t t h e presence of hydro- gen atoms does n o t modify t h e m o b i l i t y of g e o m e t r i c a l k i n k s on screw d i s l o c a t i o n s . Two hypotheses can be proposed a t t h i s p o i n t .

a ) The i n t e r a c t i o n o f t h e g e o m e t r i c a l k i n k s w i t h hydrogen atoms i s very weak. T h i s c o u l d b e due, among v a r i o u s f a c t o r s , t o a s t r o n g d e l o c a l i z a t i o n of t h e hydrogen atom i n t h e d i s l o c a t i o n environment caused by t h e s t r e s s f i e l d of d i s l o c a t i o n c o r e ( 1 6 ) . Anyway, t h e s t r e s s f i e l d h a s t h e e f f e c t of p e r t u r b i n g t h e p o t e n t i a l b a r r i e r between a d j a c e n t s i t e s i n a d i r e c t i o n p a r a l l e l t o t h e d i s l o c a t i o n l i n e and f a v o u r s t h e p i p e d i f f u s i o n a l o n g d i s l o c a t i o n l i n e s (17).

b ) The c o n c e n t r a t i o n of hydrogen atoms a l o n g t h e d i s l o c a t i o n l i n e i s very small due t o a low b i n d i n g energy between screw d i s l o c a t i o n s and hydrogen atoms ( 1 8 ) . On t h e o t h e r hand a h i g h m o b i l i t y of hydrogen atoms a l o n g t h e d i s l o c a t i o n l i n e c o u l d favour t h e f o r m a t i o n of p a i r s o f atoms c l e a r i n g up of s i n g l e atoms t h e d i s l o c a - t i o n l i n e .

However, t h e experimental r e s u l t s show some i n t e r a c t i o n between t h e s e p a i r s of hydrogeil atoms and g e o m e t r i c a l k i n k s on screw d i s l o c a t i o n s . I n f a c t , d i a t o m i c c l u s - t e r s have a lower m o b i l i t y and a b i n d i n g energy w i t h t h e d i s l o c a t i o n h i g h e r than t h o s e of hydrogen atoms. Therefore, a t low t e m p e r a t u r e s , hydrogen c l u s t e r s behave a s p i n n i n g p o i n t s f o r t h e g e o m e t r i c a l k i n k s on screw d i s l o c a t i o n s , making t h e a' com- ponent d i s a p p e a r . I n t h e temperature range of t h e SK2 component of SK(H) r e l a x a t i o n , t h e d i a t o m i c c l u s t e r s become mobile and a t t h e sane time c a p a b l e o f c o n t r o l l i n g t h e motion of t h e g e o m e t r i c a l kinks. Such i n t e r a c t i o n p r o c e s s between g e o m e t r i c a l k i n k s -hydrogen c l u s t e r s i s t h e c a u s e of a r e l a x a t i o n p r o c e s s t h a t we w i l l name SK*(H) and i s superposed upon t h e SK2 component due t o K.P.F. on non-screw d i s l o c a t i o n s , which i s a l s o c o n t r o l l e d by t h e d i f f u s i o n of c l u s t e r s of hydrogen.

Such i n t e r a c t i o n o f g e o m e t r i c a l k i n k s on screw d i s l o c a t i o n s and diatomic C ~ U S -

t e r s of hydrogen can be extremely complex because of t h e v a r i o u s p o s s i b l e o r i e n t a - t i o n s of t h e p a i r s of atoms and t h e d i f f e r e n t t y p e s o f g e o m e t r i c a l k i n k s (19). There- f o r e t h i s a s p e c t should be s t u d i e d more i n d e t a i l i n t h e f u t u r e . However we can i n - d i c a t e now t h a t t h e b i n d i n g energy g e o m e t r i c a l kink-hydrogen c l u s t e r s Eg (H-H) must be lower t h a t t h e b i n d i n g energy hydrogen c l u s t e r - n o n screw d i s l o c a t i o n EB (H-H), s i n c e t h e SK'(H) component d i s a p p e a r s through a n n e a l i n g a t lower tempera-

C8-194 JOURNAL DE PHYSIQUE

tures, and more quickly than SK2 component.

1V.- CONCLUSIONS

The co-existence of the

a '

component and the SK(H) relaxation that we observed allows us to come to the following conclusions :

a) The interaction of geometrical kinks on screw dislocations and hydrogen atoms is null or very weak.

b) The SKI component can be attributed totally to KPF on non-screw dislocations controlled by the diffusion of hydrogen atoms.

C) The interaction of geometrical kinks on screw dislocations and diatomic hydrogen clusters is noticeable and causes a relaxation peak that We will call SK'(H)- d) The SK2 component that we had noticed is the result of the superposition of

two components :

SK-(H) due to the process indicated above in c.

SIC2 itself, due to KPF on non-screw dislocations controlled by the diffusion of diatomic hydrogen clusters.

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1

.-

Takita K., Sakamoto K. ; Scripta Met. 10 (1976) 399

2

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^{Mser P}

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Dufresne J.F., Ritchie J.G.; ICIFUAS-6, Ed. R. Hasiguti, University of Tokio Press (1977) 473

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^Sakamoto K., Shimada M.; ICIFUAS-7, J. de Phys. 42 (1981) C5-109

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^{San Juan J.,} Fantozzi G., Esnouf C., Vanoni F.; Proc. Hydrogen and Materials H-3, Ed. P

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Fantozzi G., Esnouf C., Vanoni F., Bernalte A.; ECIFUAS-4, J. de Phys. 44 (1983) C9-633

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Fantozzi G., N6 M.L., Esnouf C.; To be published in J. of Phys-F Physics Metals.

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Met. Trans. 11A (1980) 861 12.- Ritchie I .G.; Scripta Met. 16 (1982) 249

13.- Vetter K., Steeb H., Kronmiiller H.; Proc. Hydrogen in Metals H-2, Paris 6-10 Juin (1977) 2C-5

14.- Bouvier- Volaille J.L., San Juan J.; ECIFUAS-4, J. de Phys. 44,(1983) C9-353 15.- Vanoni F.; Thesis University of Grenoble (1973)

16.- Fukai Y., Sugimoto H.; Advances in Physics 34 (1985) 263 17.- Kiuchi K., Mc Lellan R.B.; Acta Met. 31 (1983) 1961

18.- Wert Ch. A.; Hydrogen in Metals 11, Ed. by G. Alefeld and J. Volkl, Springer- Verlag, Berlin (1978) 305-330

19.- Seeger A., Wiithrich C.; I1 Nuovo Cirnento 33B (1976) 38

Fig.1.- Internal friction spectra before and after a weak hydrogen charging. The background has been eliminated for both spectra.

a ) a peak b e f o r e hydrogen charging

b) S-K(H) peak in the same sample after a weak charging

6

0

4..

0 0

r(

*

a

I-

d ^2.,

n

0-

Fig.2.- Curves of the shear modulus corresponding to the spectra shown in the Fig.1. The curves are shifted for in such way their values at low temperatures coincide, making their comparison easier.

-

⁺

.a**.

*.

'. ^b

pt ^a

+ t

: *

:

+

+

!

+

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'.

t ***a.

?-• _*'. '*....* *....

** **"

*.

: *.

-0.

'+.d

^C,

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4

0 50 100 150 200

TEMP. K

C8-196 JOURNAL

DE

PHYSIQUE

Fig.4.- Curves o f t h e s h e a r madulus corresponding t o t h e s p e c t r a shown i n Fig.3.

These c u r v e s have n o t been normalized. They a r e j u s t s h i f t e d f o r i n t h i s way t h e i r v a l u e a t low t e m p e r a t u r e s c o i n c i d e , making t h e i r comparison e a s i e r .

a ) A f t e r s t r o n g hydrogen charging b ) A f t e r a l o n g a n n e a l i n g a t 2 4 0 K

c ) Curve o f s h e a r modulus o f t h e former a peak

20

15..

0 0 0

4

* ^10..

<

I- J W

a

0 *

*

. ..

F++,'**,++' .

+.*+

. ^a

.*+*. ³ . .

^+++,

.

^-8.

,.' .

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^{+ + f}

^t

** + ++*+

t

-

^t*+

.

t ⁺

5..-,

_**.

.

⁺

"*

..,.*...,

^{***" +++++}

t++**t**t*+++t*+++t++.+*++*t

0 50 100 150 200 250

TEMP. K

Fig.3.- I n t e r n a l f r i c t i o n s p e c t r a a f t e r a s t o n g hydrogen charging and a n n e a l i n g a t 2 4 0 K . a ) S - K ( H ) r e l a x a t i o n a f t e r removal of t h e t r a n s i t o r y e f f e c t s by a n n e a l i n g a t 2 4 0 K . b ) S - K ( H ) r e l a x a t i o n a f t e r a l o n g a n n e a l i n g a t 2 4 0 K .